The Decorator pattern allows you to add new behavior to objects dynamically without modifying their structure. It wraps an object to enhance or alter its behavior at runtime.   Purpose To extend the functionality of objects in a flexible and reusable way without changing the original class code.   Key Characteristics Uses composition , not inheritance Decorators implement the same interface as the target object Can be stacked or chained to combine behaviors   Pros Adds behavior without modifying existing classes Supports open/closed principle Allows dynamic behavior composition   Cons Many small classes can increase complexity Can be harder to trace behavior flow when deeply nested   Use Cases Adding features like logging, security, or validation to financial operations Applying transaction fees, taxes, or discounts dynamically Decorating notifica...

The Adapter pattern converts the interface of a class into another interface the client expects. It allows incompatible interfaces to work together without modifying existing code.   Purpose To enable integration between systems or components with mismatched interfaces by translating one interface to another.   Key Characteristics Acts as a bridge between incompatible interfaces Promotes reusability of existing components Often used when integrating third-party services   Pros Supports integration with legacy or external systems Avoids rewriting existing code Promotes flexibility and modularity   Cons Adds an extra layer of abstraction Overuse can lead to complex system dependencies   Use Cases Adapting a third-party payment gateway into a common interface Converting external logging systems to your internal logger Integrating legacy financial APIs...

The Prototype pattern is used to clone an existing object rather than creating a new instance from scratch. It provides a way to copy objects while maintaining performance, especially when object creation is expensive or complex.   Purpose To reduce the cost and complexity of creating new objects by copying an existing one instead of building it step by step or with multiple dependencies.   Key Characteristics Cloning existing objects using a Clone or Copy method Typically involves deep or shallow copying Useful when object construction is expensive or slow   Pros Reduces object creation overhead Simplifies duplicating complex objects Adds flexibility by allowing modifications to a clone   Cons Cloning may be complex for deep object graphs Requires careful management of mutable shared references   Use Cases Cloning template-based documents , reports, or invoices ...